Most vehicles in operation today are powered by internal combustion (IC) engines. Internal combustion engines typically have a plurality of cylinders or other working chambers where combustion occurs. Under normal driving conditions, the torque generated by an internal combustion engine needs to vary over a wide range in order to meet the operational demands of the driver. Over the years, a number of methods of controlling internal combustion engine torque have been proposed and utilized. Some such approaches contemplate varying the effective displacement of the engine. In conventional variable displacement engine operation, a fixed set of cylinders are deactivated during low-load operating conditions. For example, an eight cylinder engine may fire all eight cylinders, then drop to a four cylinder mode (in which four cylinders are fired and four are deactivated). Cylinder deactivation during low-load operating conditions can help reduce fuel consumption.
Some approaches involve operating a variable displacement engine (VDE) in a hybrid electric vehicle. One such approach is described in the U.S. Pat. No. 7,225,782 (hereinafter referred to as the '782 patent). The '782 patent relates to a technology for controlling engine torque during transitions between VDE modes. In the invention described in the '782 patent, as the engine transitions between states involving different numbers of cylinders, the throttle is substantially adjusted to control the torque output of each cylinder.
While the above approaches work well for various applications, there are ongoing efforts to further improve fuel efficiency and engine output in hybrid powertrain systems.